The need for a clear view of the area surrounding a motor vehicle is a problem for any driver. This problem is particularly acute for the operator of a large truck because of the size of the blind spots associated therewith. The use of numerous and large mirrors have helped to alleviate this problem. One blind spot that remains, however, is close to the truck on the passenger side of the cab. In an attempt to alleviate such a problem a window is sometimes positioned near the bottom of the passenger side door. Such a window only reduces the size of the blind spot, however, rather than eliminating it. Blind spots still exist in front of, in back of, and directly below the window.
In order to further improve the driver's field of view a lens may be placed in the window. Such a lens is typically a Fresnel lens in order to conserve space. An example of a Fresnel lens that could be used to widen the viewing angle is the lens sold by Minnesota Mining and Manufacturing Company under the trademark "Vanguard." The Vanguard lens is a circular Fresnel lens, designed for use in the rear window of a van to provide wide angle viewing. A disadvantage of the Vanguard type lens lies in its circular symmetry. When the focal length of the lens is shortened to the degree required to provide adequate wide angle viewing in a horizontal plane, the effective viewing area is confined to a small portion of the lens. This problem is accentuated when, as is commonly the case, the lens is rectangular with the shorter dimension extending in the plane where greater wide angle viewing is required.